A study of hexokinases and sugar dehydrogenases of Limulus polyphemus has shown that the predominant hexokinase of the hepatopancreas, a fructomannokinase, has little ability to catalyze the phosphorylation of glucose. The hepatopancreas also has smaller quantities of two typical hexokinases each with a very low Km for glucose and mannose and a high Km for fructose. In contrast the chief, very active hexokinase of Limulus muscle has great affinity for glucose and mannose and little for fructose. Muscle also has small quantities of the fructomannokinase and a second low Km hexokinase. A D-xylose-NADP dehydrogenase capable also of using glucose, galactose and other sugars to a lesser extent, is much more active in hepatopancreas than in muscle. A NAD(P)-dehydrogenase, using L-fucose, D-arabinose and L-galactose and not active with any other sugar tested occurs chiefly in the hepatopancreas. The results are in accord with earlier conclusions about the relative importance of muscle in glucose metabolism in Limulus.